The reservoir or lake of a dam may carry much sludge or sand from the upstream of the lake. The sludge or sand should be removed to prevent from its accumulation in the lake. Conventional removing method relies upon the water pump which may deliver the muddy or sandy water as driven by electric motor or diesel engine. The power or oil will then be consumed. The conventional pump may be damaged by the coarser sand or stones. The friction between the sand and the pump impeller may deteriorate the pump and shorten the service life of pump. By considering the safety operation of a pump, the sand or sludge concentration in carrying water should be controlled in a limited value so that the sludge or sand discharging rate will then be reduced. If for pumping much quantity of sludge or sand, much power or energy must be spent to increase the handling capacity and quantity of discharged water whereby the water within the reservoir will be greatly wasted.
The present inventor has found these defects and researched to disclose the present invention.